Low pressure mercury vapour discharge lamp including an alloy type getter coating



United States Patent Teizo Hanada Saitama-ken;

Tadaaki Watanabe, Hyogo-ken; Kenii Enokida; Shunji Kikuchi; AkiraSomeya,

Inventors Yokohama-shi, Japan Appl. No. 795,314 Filed Jan. 30, 1969Patented Dec. 22, 1970 Assignee Tokyo Shibaura Electric Co., Ltd.Kawasaki-shi, Japan a corporation of Japan Priority Feb. 3, 1968 JapanNo. 43/6427 LOW PRESSURE MERCURY VAPOUR DISCHARGE LAMP INCLUDING ANALLOY TYPE GETTER COATING 8 Claims, 4 Drawing Figs.

U.S. Cl 313/178, 313/109, 313/179, 313/185 Int. Cl ..H01j 61/20,

[50] Field ofSearch 313/109, 174,176, 178, 185,179

[56] References Cited UNITED STATES PATENTS 2,444,423 7/1948 Braunsdorff313/178 2,769,112 10/1956 Heine et a1 313/109X 2,855,368 10/1958Perdijk, Jr., et al..... 252/18l.6

2,885,587 5/1959 Wainio et al 313/109X 2,959,702 11/1960 Beese 313/1093,308,329 3/1967 Foreman et al 313/107 Primary Examiner-James W.Lawrence Assistant Examiner-Palmer C. Demeo Attorney-George B. OujevolkABSTRACT: A low pressure mercury vapor discharge lamp with reducedgeneration of end bands and with no increase in the occurrence of anodespots, including a getter comprising an alloy of at least one selectedfrom a first group consisting of nickel, cobalt, iron, aluminum andcopper and at least one selected from a second group consisting oftitanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum,scandium, cerium and tungsten, said alloy excluding a titaniumnickelalloy.

LOW PRESSURE MERUURY VAPOUR DISC 1 1' GE LAMP INCLUDING AN ALLOY TYPEGET'IER COAG This invention relates to low-pressure discharge lamps andmore particularly to a low-pressure mercury vapor discharge lamp havinggetters which reduce the formation of an end band and which prevent theformation of an anode spot from being increased.

Among low-pressure mercury vapor discharge lamps are an ordinaryfluorescent lamp for illumination, black light lamps, sterilizationlamps, erythemal fluorescent lamps and the like, which are dischargelamps operative under low-pressure mercury vapor.

In the low-pressure mercury vapor discharge lamp of this nature,blackenings are caused at the ends of the sealed envelope. Suchphenomena are classified into an end band and an anode spot. The formeris caused when a mercury oxide formed by the reaction of mercury withthe oxygen ejected from an electron-emitting substance during lightingof the lamp is deposited on that part of the inner surface of the sealedenvelope which faces a Faraday's dark space'having a small potentialgradient, while the latter phenomenon is caused by the spattering of theelectron-emitting substance on that part of the inner surface of sealedenvelope which faces the electrodes.

This blackening damages the appearance of a low-pressure mercury vapordischarge lamp and reduces an available amount of light. The inventorshave previously proposed the use of an alloy which acts as a getter andwhich includes major components of titanium and nickel with a view toeliminating the above drawbacks and to reduce the generation of the endhand without accelerating the generation of the anode spot. it has beenfound through experiments that various alloys can be employed as gettersfor use in a vapour mercury vapor discharge lamp in addition to atitanium-nickel alloy.

An object of this invention is to provide a low-pressure mercury vapordischarge lamp including'getters formed of an alloy other than atitanium-nickel alloy and which adsorb the oxygen generated from aneIectron-emissive material during lighting of the lamp, to reduce theformation of an end band and yet to avoid an increase in the formationof an anode spot.

This invention thus provides a low-pressure mercury vapor discharge lampcomprising a light-transmissive sealed envelope, a quantity of mercuryand starting rare gas sealed in said envelope, and a pair of electrodemounts sealed to both ends of said envelope, said electrode mounts eachsupporting a filament coated with activated electron-emitting materials,by comprising a getter including an alloy which is formed of at leastone selected from a first group consisting of nickel, cobalt, iron,aluminum and copper and at least one selected from a second groupconsisting of titanium, zirconium, hafnium, thorium, vanadium, niobium,tantalum, scandium, cerium and tungsten, said alloy excluding atitanium-nickel alloy, said getter being disposed on said mounts exceptthose portions thereof which are coated with the activatedelectron-emitting materials and those portions thereof which aremaintained at operation temperatures lower than 300 C. and higher thanthe melting point of said alloy.

According to the feature of the invention, getters are formed of analloy including main components of at least one metal selected from afirst group consisting of nickel, cobalt, iron, aluminum and copper, andat least one metal selected form a second group consisting of titanium,zirconium, hafnium, thorium, vanadium, niobium, tantalum, scandium,cerium and tungsten, said alloy excluding a titanium-nickel alloy, anand such getters are disposed on portions of electrode mounts or in thevicinity thereof other than those coated with an electron-emissivesubstance, and which are held at temperatures higher that than 300 C.and lower than the melting point of the alloy.

The metals falling under said first group have a good electricalconductivity, and those belonging to said second group have a strongactivity and a getter action. A low-pressure mercury vapor dischargelamp having getters formed of an alloy of metals in these two groupseliminates or reduces the formation of an end band and keeps theformation of an anode spot to an extent not exceeding that in a priorart low-pressure discharge lamp using no getters.

The invention can be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. l is a schematic plan, partly in section, of a circular fluorescentlamp embodying the low-pressure mercury vapor discharge lamp of thisinvention;

H6. 2 is a side elevation, partly in section, of a part of the lampshown in FIG. 1 to illustrate an electrode mount;

FIG. 3 is a perspective view of a modification of the electrode mount;and

FIG. 4 is a perspective view of a further modification of the electrodemount.

The low-pressure mercury vapor discharge lamp shown in FIGS. 1 and 2 isillustrated as a circular fluorescent lamp having a rated wattage of 30w. The fluorescent lamp comprises a cylindrical glass envelope 1 havingan inner wall surface deposited with fluorescent materials,'and a pairof electrode mounts 2 (one of them is shown in the FIGS.) sealed to bothends of said envelope l, each said electrode mount including a flaredglass stem 3 hermetically sealed to said envelope l, and a pair oflead-in wires 5 and 6 which penetrate through said stem 3 so that theirinner ends define inner-lead wires. The inner-lead wires mechanicallyclamp a filament 7 which is coated with an activated electron-emittingmaterial such as BaO-SrO-CaO containing MgZrO A base shell 8 having twopairs of base pins (Only one of each pair is shown in FIG. 1.) is

fitted to the outer portion of the stem 3, and the lead-in wires 5 and 6are respectively connected to one pair of the pins. Getters l2 and 13are disposed on the surfaces of the innerlead wires at predeterminedportions thereof. The getter consists of an alloy, as preferred examplesthereof are hereinbelow mentioned, comprising at least one metalselected form from a first group consisting of nickel, cobalt, iron,aluminum and copper, and at least one metal selected from a second groupconsisting of titanium, zirconium, hafnium, thorium, vanadium, niobium,tantalum, scandium, cerium and tungsten. (a titanium-nickel alloy beingexcluded.) Deposition of the alloy may be carried out by firstpulverizing the alloy, and then allowing the alloy powder obtained to besuspended in a binder solution consisting of nitrocellulose and butylacetate. The suspension is deposited on the surface of the inner-leadwires 5 and 6 along predetermined lengths thereof.

FIG. 3 shows a modification of the electrode mount employed in thedischarge lamp of this invention. The mount illustrated comprises aflared glass stem 30, a pair of lead-in wires 31 and 32 penetratingthrough the stem 30 and connected to base pins mounted on a base shell(not shown), a filament 33 bridged between the lead-in wires 31 and 32with its ends clamped at the inner ends of the lead-in wires 31 and 32,and wire anodes 34 and 35 attached to the lead-in wires 31 and 32. Onthe wire anodes 3d and 35 are coated with getters 36 and 37.

FIG. 4 shows a further modification of the electrode mount, in which areprovided a flared stem 40, a pair of lead-in wires 41 and 42 and afilament 43. In this modification, a shield electrode 44 is disposedsuch that it surrounds the filament 43. The shield electrode M isplanted in the stem 40 by a support wire 45, and has a getter 36 coatedon the surface thereof.

Places upon which the getter is formed are not limited to those shown inthe foregoing examples. The getter may be formed on the surface of theflared stem 3, 30 or 40.

The getter in accordance with this invention is formed of an alloy of atleast one metal selected from a first group consisting of nickel,cobalt, iron, aluminum and copper, and at least one metal selected froma second group consisting of titanium, zirconium, hafnium, thorium,vanadium, niobium, tantalum, scandium, cerium and tungsten, said alloyexcluding a titanium-nickel alloy. The metals belonging to the firstgroup are good electrical conductors, while the metals falling in thesecond group have a strong activity and hence a getter action.

An alloy consisting of metals in the both groups eliminates or reducesthe formation of an end band in a low-pressure mercury vapor dischargelamp and does not tend to increase an anode'spot.

In contrast, when at least one metal selected only from the second groupis employed as a getter, such will not only be inefiective to thereduction of the end band but also accelerate the production of theanode spot. This is believed due to the following reasons.

The metals belonging to the second group have a gas adsorption property.But, when these metals only are used as getters in a low-pressuremercury vapor discharge lamp, the getter thus formed adsorbs both gasesejected from fluorescent materials and the envelope during thefabricating process of the lamp and, in particular, during theevacuation process thereof, and gases produced at the time ofdecomposition of electron-emissive materials, and no longer has anadsorption power as it is saturated by the time the manufacturingprocess of the lamp is complete. Further, the metal forming the getterspatters when tired and is deposited on the fluorescent materials, thusgiving rise to the formation of the anode spot. Even if the metal isprevented in adsorptivity from being saturated, free barium in theelectron-emissive material will become excessive since the metal isstrongly deoxidizing, whereby the formation of the anode spot isaccelerated.

In case, as in the present invention, there is employed an alloy of atleast one metal of strong activity, selected from the first group and atleast one metal selected from the second group, since the latter groupmetals are good electrical conductivity, generation of end bands isdecreased while that of anode spots is prevented from increasing, forthe reasons set forth below.

The getter action of the second group metal, namely, an oxygen adsorbingaction in this case, is suitably controlled by the interposition of ametallic powder of the first group metal, so that no saturation of thegetter takes place during the evacuation process of the lamp. Further,the adsorbed oxygen is gradually diffused into the interior of thedeposited getter due to the metallic powder of the first group metal,with the result that the adsorption power at the surface layer portionof the getter is recovered thereby causing the getter to always exhibitits oxygen adsorption power. This is believed to be effective forpreventing the formation of the end band. It is also believed that,since the metallic powder of the second group metal is surrounded by thefirst group metal having a high electrical conductivity, a temperaturerise in an anode cycle can be suppressed whereby an excess temperaturerise of the cathode spot in cathode cycle is avoided to give no adverseeffect on the anode spot.

An alloy formed of at least one metal selected from the first group andat least one metal selected from the second group forms no amalgam whenit reacts with the mercury contained in the sealed envelope, and isresistive against electron or ion bombardment.

The alloy formed in accordance with this invention must be disposed onsuch places that are on or in the vicinity of the electrode mountsexcepting portions coated with electronemissive material, and that arekept during operation at temperatures higher than 300 C. and lower thanthe melting point of the alloy. If the alloy is disposed or applied on aportion coated with the electron-emissive material, electron emissivitywill be hindered. Similarly, when the alloy is deposited on a placewhose operation temperature is lower than 300 C. the alloy has a smallgas adsorption power and does not adsorb a required amount of the oxygenemitted during lighting, so that no expected result is obtained. On theother hand, depositing the alloy on a portion above the melting point ofthe alloy will cause the alloy to eject gases and then to vapor to bedeposited on the fluorescent layer, thus accelerating the formation ofan anode spot. In order to eliminate these defects, portions to becoated with the alloy should preferably be those maintained at atemperature lower than the melting point of the alloy by more than about100 C. Selection of places whose temperature in the operation of thelamp is within the range of 400 C. and 800 C. generally achieves goodresults for this purpose. The alloy may be deposited on the inner-leadwires of electrode mounts, the leg portions of an electrode coil, orwhere an anode or a shield is employed, on the surface thereof, or onother members provided separately from electrode mounts.

The table below shows examples of the alloy, in which the term end bandindex represents the degree of formation of an end band by way of10-point method. Index 10 thus represents the complete absence of theend band; index 7 represents that the formation of the end band isclearly observed; and index 5 or smaller represents that the lamp inoperation is considerably detracted in visual appeal due to theprominent formation of the end hand. All the samples in the table arecircular fluorescent lamps having a rated wattage of 30 w.

Melting Alloy eompositemper- Lighting End tion, weight ature, period,band percent hours index Example N 0.:

1 Al 11, Zr 89 1,350 6,000 10 2- Go 38, Ti 62 1,070 6, 000 9-8 3 Cu 60,Ti 40 975 3,000 10 4 Ni 50, Ta 50 1, 545 6,000 8 5 Ni 65,W 35 1,5056,000 8 6 Zr76,Ni24 1,200 3,000 10 7 Th 66, Ni 34 1, 150 6,000 9-8 8 Zr32, Cu 68 1,115 3, 000 10 9 Ce 56, Fe 44 1,180 3,000 10 For the purposeof comparison, a lamp deposited with a Ti powder was produced. It showedan end band index of 10 after a lighting period of hours, but aconsiderable amount of anode spot was formed.

Similarly, a lamp fabricated without the deposition of the getter alloyexhibited an end band index of 8 to 7 after a lighting period of 2,000hours, and an end band index of 5 to 4 after a lighting period of 6,000hours.

As will be appreciated from the comparisons given above, a low-pressuremercury vapor discharge lamp including getters formed of an alloy asspecified herein has improved characteristic regarding the formation ofan end band, and yet has a similar property to that of a conventionaldischarge lamp with no getter disposed, regarding the formation of ananode spot.

It was observed that discharge lamps in examples 3, 6, 8 and 9 producedanode spots to a similar extent to that in a prior art low-pressuremercury discharge lamp.

Alloys used in the foregoing examples are those formed of one metalselected from the first group and one metal selected from the secondgroup. But more than one metal selected from either one of the groups orfrom the both groups may be alloyed to form getters.

We claim:

1. A low-pressure mercury vapor discharge lamp comprising alight-transmissive sealed envelope, a quantity of mercury and startingrare gas sealed in said envelope, and a pair of electrode mounts sealedto both ends of said envelope, said electrode mounts each supporting afilament coated with activated electron-emitting materials,characterized by comprising a getter including an alloy which is formedof at least one selected from a first group consisting of nickel,cobalt, iron, aluminum and copper and at least one selected from asecond group consisting of titanium, zirconium, hafnium, thorium,vanadium, niobium, tantalum, scandium, cerium and tungsten, said alloyexcluding a titanium-nickel alloy, said getter being disposed on saidmounts except those portions thereof which are coated with the activatedelectron-emitting materials and those portions thereof which aremaintained at operation temperatures lower than 300 C. and higher thanthe melting point of said alloy.

2. The low-pressure mercury vapor discharge lamp according to claim 1,said alloy consisting of 11 percent by weight of aluminum and 89 percentby weight of zirconium.

6 ing to claim 1, said alloy consisting of 66 percent by weight ofthorium and 34 percent by weight of nickel.

7. The low-pressure mercury vapor discharge lamp according to claim 1,said getter being disposed on a pair of anode wires which are providedon each of said mounts.

8. The low-pressure mercury vapor discharge lamp according claim 1, saidgetter being disposed on a shield electrode which is provided on each ofsaid mounts.

